The present invention relates to an image forming apparatus employing an electrophotographic system such as a copying machine, a printer and a facsimile machine, and in particular, to a color image forming apparatus wherein toner images formed on a plurality of image carriers by a plurality of image carriers, latent image forming means and developing means are primarily transferred onto an intermediate transfer object, and then, are secondarily transferred onto a recording sheet.
In the case of a conventional color image forming apparatus employing an electrophotographic system, there have been proposed various types of systems wherein a plurality of image forming sections are arranged in parallel in the conveyance direction, and toner images each being different from others in terms of color formed respectively on photoreceptor drums in image forming sections are successively transferred on a recording sheet held on a transfer belt.
There is also known a color image forming apparatus wherein a transfer drum around which a recording sheet fed from a sheet feeding section is wound is used in place of the transfer belt stated above. By transferring toner images visualized by developing means onto the recording sheet wound around the transfer drum successively, a full color image is formed on the recording sheet. After this, the recording sheet is separated from the transfer drum and is subjected to fixing of the toner image conducted by a fixing means to be ejected out.
Further, in another color image forming apparatus, there is also proposed a system wherein a plurality of image forming sections are arranged in parallel, toner images each being different from others in terms of color formed respectively on photoreceptor drums in image forming sections are successively transferred onto an intermediate transfer object for forming superposed primary transfer images, and the primary transfer images are transferred onto a recording sheet held on a conveyance belt.
A color image forming apparatus of a tandem type of this kind having a plurality of photoreceptors wherein a color image is formed through one turn of each of plural photoreceptors can output full color images at higher speed, compared with a color forming apparatus of a multi-rotation type wherein a color image is formed through plural turns of a single photoreceptor.
A plurality of photoreceptors and intermediate transfer objects need to be removed from an apparatus main body because of their maintenance and life-times. Therefore, the structure which makes it easy to remove a plurality of photoreceptors and intermediate transfer objects has been required by the color image forming apparatus of a tandem type.
Since a plurality of photoreceptors, intermediate transfer objects in particular, rotating means to rotate the intermediate transfer objects, and intermediate transfer units including primary transfer means have considerable mass, it has been difficult for a user to draw out plural photoreceptors from positions where the photoreceptors have been mounted in the apparatus main body, and to take out directly intermediate transfer units from positions where the intermediate transfer units have been mounted in the apparatus main body, because it has been difficult to apply the physical power. In particular, it is not easy to pull out the heavy unit horizontally toward the front side of the apparatus main body. Furthermore, a unit such as a photoreceptor and an intermediate transfer object is weak against an impact, and there is a risk that the unit becomes unusable if a part of the unit is touched while it is pulled out. A scratch caused by a shock not only affects images in image forming in a single color but also has possibility that a desired color cannot be reproduced in color image forming, and the scratch turns out to be a fatal defect for a color image forming apparatus.
On the other hand, when each member is provided with its own mechanism to take out each member without interference, a large number of taking-out mechanisms (for example, slide rail mechanisms) are needed. Each taking-out mechanism requires its strength that withstands the weight. This makes an entire apparatus to be large.
The more the mechanism to take out each member individually is increased, the more difficult the positional adjustment between members is. In an image forming apparatus having plural photoreceptors, in particular, it is necessary to conduct superposition of each color in extremely high accuracy. If mutual positional deviation is caused for each maintenance of a unit, it is not possible to reproduce the color desired by a user. Furthermore, an intermediate transfer object is a member on which color toner images each being of a different color are superposed, and relative positions of intermediate transfer objects for plural photoreceptor drums are required to be accurate.
Further, when a color image forming unit of this kind is provided on a copying machine, there are further caused problems. Since a document image reading apparatus is arranged on the upper portion of the copying machine, there is needed a complicated opening/closing mechanism which opens the document image reading apparatus from the upper portion of the apparatus main body. Each of the document image reading apparatus and the opening/closing mechanism has considerable mass, and how to handle them is a problem. If an impact is applied on the document image reading apparatus in the course of opening/closing operations, there are caused problems of difficulty in maintaining accuracy of optical members, parts damages and injures of an operators. Drawing out from the upper portion of the apparatus main body has the aforesaid problems, although it is easy for a user to apply the physical power.
In the image forming apparatus which forms images on both sides of a sheet, a sheet fed from the a sheet feeding means is subjected to transfer and fixing of toner images formed on an image carrier on the first surface of the sheet, and then is branched from the sheet ejection path to be conveyed to a reversing means provided on the lower or upper portion. The sheet thus conveyed is reversed up side down, and then, is made to join a sheet conveyance path again from a sheet feeding section. The sheet which has joined the sheet conveyance path is conveyed to the image carrier again so that a toner image may be transferred onto the second surface of the sheet.
As a method to form images on a sheet from inputted multi-color images, TOKKAIHEI No. 9-006083 discloses an image forming apparatus wherein a plurality of developing units are arranged in parallel on one side of an image carrier representing a belt arranged longitudinally, and a sheet ejection section is provided on the other side, and charging, writing of a latent image and developing are conducted in succession within one turn of one image carrier.
In an image forming apparatus for a color image, when an image carrier on which a toner image is formed and a developing unit are arranged in the longitudinal direction, if joining from the reversing means is conducted in the vicinity of the sheet feeding unit positioned at the lower portion, the image forming apparatus is made to be large in the longitudinal direction, which is a problem.
For example, FIG. 9 is an illustrative diagram of an image forming apparatus showing image forming flows to both sides of a sheet.
In FIG. 9, image forming apparatus 101 is provided with scanner section R, image carrier 110, scorotron charging unit 111, image writing means 112, developing unit 113, transfer means 115, fixing means H, sheet feeding section 117, bypass sheet feeding section 109, reversing means S and with sheet ejection tray T.
The scanner section R reads an image of a document set through an optical system. The image writing means 112 exposes image carrier 110 to light to form a latent image, based on the image read. The latent image formed on the image carrier 110 is developed by developing unit 113 to turn into toner.
On the other hand, the sheet feeding section 117 is provided with a plurality of sheet feeding units 117a-117d each housing therein sheets in a different size, and a sheet is fed out toward registration roller 141 through first sheet conveyance path P0 by sheet feeding roller 118a of the selected sheet feeding unit, for example, of sheet feeding unit 117a. The registration roller 141 starts rotating to convey the sheet so that the toner image formed on the image carrier 110 may be synchronized with the sheet.
The sheet conveyed to the registration roller 141 is superposed on the toner image formed on the image carrier 110, and thus, the toner image is transferred onto the sheet. The sheet on which the toner image has been transferred is sent to fixing means H to be fixed, and is ejected to sheet ejection tray T.
When transferring a toner image on the second surface of the sheet on which the toner image has been transferred onto the first surface thereof, the sheet on which the toner image has been formed is fed in second sheet conveyance path G.
On the second sheet conveyance path G, there is provided reversing means S that is equipped with a pair of switchback rollers 143 capable of rotating regularly and inversely and guide 148. The sheet which has been fed in is reversed inside out by switching of the sheet conveyance direction for the switchback rollers 143 c of the reversing means S and switching of the conveyance path of guide 148. The sheet thus reversed is sent to roller unit 118e by driving rollers 144 and 145 to join the first sheet conveyance path P0 representing a sheet conveyance path from the sheet feeding section. The sheet which has joined the first sheet conveyance path P0 is sent again to the registration roller 141, and then, is ejected to sheet ejection tray T after the toner image formed on the image carrier is transferred onto the second surface of the sheet and fixed.
Namely, in the conventional image forming apparatus, when forming toner images on both sides of a sheet, the sheet on which a toner image has been transferred on the first surface thereof is reversed inside out by the reversing means, and is made to join the sheet conveyance path coming from the sheet feeding section, and after that, a toner image is transferred onto the second surface of the sheet.
From viewpoints of production cost and easiness of design for an image forming apparatus, the reversed sheet has been made to join the sheet conveyance path in the vicinity of a sheet feeding unit by a roller similar to that of the sheet feeding unit. For example, one sheet feeding unit among plural sheet feeding units has been removed to be used for the reversed sheet to join the conveyance path.
For this reason, when an image carrier on which a toner image is formed and a developing unit are arranged in the longitudinal direction, if joining from the reversing means is conducted in the vicinity of the sheet feeding unit positioned at the lower portion, the image forming apparatus is further made to be large in the longitudinal direction.
When the time for image forming on both sides of a sheet needs to be shortened, the conveyance time for conveying the reversed sheet to the vicinity of the sheet feeding section is a problem.
The invention has been achieved to solve the aforesaid problems, and an object of the invention is, in a color image forming apparatus having a plurality of photoreceptors and intermediate transfer units, to make operations for mounting the aforesaid members and image forming means such as developing means on an apparatus main body and operations for dismounting them from an apparatus main body to be easy and to make maintenance for them to be easy, and to realize prevention of troubles of each member, high accuracy of positions and down-sizing of the total apparatus.
Another object is to reduce a floor space of an apparatus and to reduce a height of an apparatus in the vertical direction, and thereby to realize down-sizing of the total apparatus.
Further object is to shorten the time for image forming on both sides of a sheet and to provide an image forming apparatus requiring less floor space.
The objects stated above are realized by either one of the following structures.
(1) A color image-forming apparatus, comprising: a plurality of image carriers; a plurality of latent image forming devices to form electrostatic latent images on the image carriers; a plurality of developing devices to develop the electrostatic latent images with toner to form visible toner images on the image carriers; an intermediate transfer member, a longitudinal direction of which is arranged at substantially a vertical direction, and onto which the toner images formed on the image carriers are sequentially transferred in such a manner that the toner images overlap relative to each other so as to form a color toner image on the intermediate transfer member; and a transferring device to transfer the color toner image formed on the intermediate transfer member onto a transfer sheet; wherein at least the intermediate transfer member and the image carriers are integrated into a rack, and the rack is drawable in substantially a horizontal direction in respect to a mainframe of the color image-forming apparatus.
(2) A color image-forming apparatus, comprising: a plurality of image carriers; a plurality of latent image forming devices to form electrostatic latent images on the image carriers; a plurality of developing devices to develop the electrostatic latent images with toner to form visible toner images on the image carriers; an intermediate transfer member to bear a color toner image formed by superimposing the toner images, which are sequentially transferred onto the intermediate transfer member from the image carriers; and a transferring device to transfer the color toner image formed on the intermediate transfer member onto a transfer sheet; wherein at least the intermediate transfer member and the image carriers are integrated into a rack, and the rack is drawable in substantially a horizontal direction in respect to a mainframe of the color image-forming apparatus.
(3) A color image-forming apparatus, comprising: a plurality of image carriers; a plurality of latent image forming devices to form electrostatic latent images on the image carriers; a plurality of developing devices to develop the electrostatic latent images with toner to form visible toner images on the image carriers; an intermediate transfer member, a longitudinal direction of which is arranged at substantially a vertical direction, and onto which the toner images formed on the image carriers are sequentially transferred in such a manner that the toner images overlap relative to each other so as to form a color toner image on the intermediate transfer member; a sheet feeding section to store a transfer sheet and to feed the transfer sheet stored; a first sheet conveyance path, through which the transfer sheet, fed from the sheet feeding section, is conveyed to the intermediate transfer member; a transferring device to transfer the color toner image formed on the intermediate transfer member onto the transfer sheet; a reversing device to reverse a front side back of the transfer sheet, onto a first surface of which the color toner image is already transferred; and a second sheet conveyance path, through which the transfer sheet, reversed by the reversing device, is conveyed to a confluent position with the first sheet conveyance path, so that the transfer sheet re-enters the first sheet conveyance path from the confluent position; wherein the confluent position, at which the second sheet conveyance path joins the first sheet conveyance path, is located at substantially a center of the sheet feeding section and at substantially a lower position of the image carriers.
(4) A color image-forming apparatus, comprising: a plurality of image carriers; a plurality of latent image forming devices to form electrostatic latent images on the image carriers; a plurality of developing devices to develop the electrostatic latent images with toner to form visible toner images on the image carriers; an intermediate transfer member, a longitudinal direction of which is arranged at substantially a vertical direction, and onto which the toner images formed on the image carriers are sequentially transferred in such a manner that the toner images overlap relative to each other so as to form a color toner image on the intermediate transfer member; a sheet feeding section to store a transfer sheet and to feed the transfer sheet stored; a first sheet conveyance path, through which the transfer sheet, fed from the sheet feeding section, is conveyed to the intermediate transfer member; and a transferring device to transfer the color toner image formed on the intermediate transfer member onto the transfer sheet; wherein the intermediate transfer member is located at substantially a upper position of the sheet feeding section, and the transferring device is shaped in a roller and contacts a lower portion of the intermediate transfer member.